This application claims the priority of German Patent Document 199 53 522.1, filed in Germany, Nov. 5, 1999, the disclosures of which is expressly incorporated by reference herein.
The invention relates to a process for the manufacture of a large area sheet metal part, in particular a body component for a vehicle, from a flat blank.
Large area body components, like vehicle roofs, outside door panels, side parts, outside cover plates or the like, are traditionally manufactured by deep drawing. Deep drawing takes place in hydraulic or mechanical drawing presses. In the deep drawing process a flat trimmed sheet metal part, the blank, is inserted into a conventional forming tool and deformed by elongation and compression in a cavity. In the case of large area sheet metal parts that are fabricated thus it has been demonstrated that in particular a slight arch renders the central region of its surface area relatively weak. Hence these large area sheet metal parts exhibit only slight resistance to buckling.
Furthermore, there exists hydromechanical deep drawing (hydromech process) for the manufacture of sheet metal parts. In this process no die impression is required, rather the drawing punch moves the clamped blank into an active medium (water) filled vessel that replaces the die impression. The water pressure causes the sheet metal to adapt to the shape of the drawing punch. In a variant of this process, the clamped blank is freely prestretched before the actual shaping deformation process in order to obtain increased ironing and thus greater strength in the blank center. To date this process has required complicated and thus expensive equipment; and the cycle times are longer compared to those of the deep drawing process.
The object of the invention is to provide a process for the manufacture of large area sheet metal parts from a flat blank. Said process makes it possible to reduce the cycle times while raising the buckling resistance in the center of the blank.
The invention solves this problem with a process for the manufacture of a large area sheet metal part, in particular a body component for a vehicle, from a flat blank, characterized in that one sided pressurization with an active medium in a forming tool gives the flat blank a prestretched preform, and that then the preform, removed from the forming tool, is formed into the final shape in a separate deep drawing tool. Other advantageous features of the invention are disclosed herein and in the claims.
The primary advantages of the invention lie in the fact that by combining for the first time two known processes, namely prestretching of an initially flat blank with an active medium to cold harden in particular the blank center and the conventional pressing (deep drawing) of sheet metal parts, one can profit from the advantages of both processesxe2x80x94optimal component properties and high process efficiency.
The prestretched sheets can be manufactured on systems with relatively low shear forces, since the maximum required pressure is approx. 15 bar. Furthermore, mechanical pressing can be used. The high pressure, which is required for conventional hydromechanical final forming and which in turn results in high press closing forces, is not necessary for the inventive process, since the final forming is done here conventionally. Since prestretching consumes very little time, as compared to the hydromechanical final forming, the cycle time for the process of the invention is significantly reduced.
The manufacture of prestretched sheet metal can be conceived as a first operation in an interconnected press train. Moreover, it is conceivable that the semifinished product manufacturer delivers to the pressing works already prestretched blanks (comparable to tailored blanks).
The use of tailored blanks is also conceivable for further reducing the weight. In this case a reinforcement, especially, e.g., in the region of the thinner sheet, can be used for locally increasing the resistance to buckling (example floor panel, tunnel, floor panel).
Prestretched blanks can also be used in soft tools, which are commonly used in prototyping. To date it was not possible to deform hydromechanically produced parts with so-called soft tools on account of the pressure that was generated.
Suitable components are all parts of the exterior skin. In addition, it seems logical to use the aforementioned process combination for all surface components, which are manufactured in any event from relatively thin sheet metal.
The inventive process can result in higher component strength, which in turn offers a potential weight reduction through the use of thinner sheet metal without having to accept the past drawbacks of hydromechanically formed sheetsxe2x80x94very high process cycle time and high system costs. Cycle times, comparable to the conventional sheet forming processes, can be targeted. The preformed blanks can be produced separately, for example, at the semi-finished product manufacturer. Thus, it is also possible to apply the process to prototype components, since the cost is virtually neutral.
One embodiment of the invention is depicted in the drawings and is explained in detail in the description.